Staff: Mentor

As the nasa website is very unreliable (at least for me)*:

The Kepler-186 system is home to Kepler-186f, the first validated Earth-size planet orbiting a distant star in the habitable zone—a range of distance from a star where liquid water might pool on the planet's surface. The discovery of Kepler-186f confirms that Earth-size planets exist in the habitable zones of other stars and signals a significant step toward finding a world similar to Earth.

The size of Kepler-186f is known to be less ten percent larger than Earth, but its mass and composition are not known. Kepler-186f orbits its star once every 130 days, receiving one-third the heat energy that Earth does from the sun. This places the planet near the outer edge of the habitable zone.

*edit, clarification: I cannot reach the website sometimes due to DNS server issues. This is a technical issue and has nothing to with the content.

The habitable zone can be calculated for any star. If you know the luminosity of the star then it is merely a simple calculation:

ri = √ (Star's Luminosity / 1.1)
ro = √ (Star's Luminosity / 0.53)​

According to the paper where the discovery was announced the luminosity of the Kepler-186 M1V star is 0.0412. Which puts the habitable zone of the star at between 0.19353 AU and 0.27881 AU. Yet the paper places the semi-major axis of the planet at 0.3926 AU. Well outside the habitable zone of the star.

The units do not fit (they do fit in the source, however), and the numerical constant of 0.53 would indicate a precision the current models do not have.

I guess that would make things even worse due to extreme seasonal variations (together with issues like the long-term stability of the orbit) - and the average would still be similar.

What do you mean "the units do not fit?" I am using their data from their paper, and the planet does not fall within the habitable zone of the star. Not by a long shot. Despite their claims to the contrary. Apparently they are more interested in publicity than actual science.

Staff: Mentor

r is a length and needs a unit of length (like meters or AU), unless you specify something like "in meters" or (here) "in AU". The same applies to the luminosity.

I am using their data from their paper, and the planet does not fall within the habitable zone of the star. Not by a long shot. Despite their claims to the contrary. Apparently they are more interested in publicity than actual science.

The claim comes from the Kepler collaboration and they are certainly interested in actual science. That leaves multiple possible options:
- error from Kepler
- error from Tom E. Morris (or the sources he bases his formulas on)
- error from you combining both
- error in our interpretation, as an example the definition of "habitable zone" varies a bit between different scientists
- something else (there is always something else)

The claim comes from the Kepler collaboration and they are certainly interested in actual science. That leaves multiple possible options:
- error from Kepler
- error from Tom E. Morris (or the sources he bases his formulas on)
- error from you combining both
- error in our interpretation, as an example the definition of "habitable zone" varies a bit between different scientists
- something else (there is always something else)

I am using only the data the discoverer's provided in their paper. I am not taking any other source. There are actually several different sources for Kelper-186 and Kepler-186f, and they do not all have the same data in common. Which is why I specifically chose to use their source paper and their data.

If they want to redefine the size of a habitable zone around a star, fine. But at the very least they could have explained why in this particular case they are expanding it to include this exoplanet. It should not be expanded merely because they want to be the first to find an Earth-like exoplanet. They call that sensationalism, not science.

When you find an error in my math, then you can rightly blame me. However, if my math is correct and I provided the sources for both the calculations and the data, then I am hardly to blame. Your hostility towards me is misplaced.

The distance from the star alone may not exclude it from habitability. depending on the composition of the atmosphere. if it has a very thick CO2 atmosphere it could still maintain suitable temperatures for plant life. Being further away from its star might also be a benefit as it might not be tially locked.

Staff: Mentor

I don't get the original publication to load here, but I assume the wikipedia editors managed to copy the numbers correctly:

The habitable zone for this system is estimated conservatively to extend over distances receiving from 88% to 25% of Earth's illumination (from 0.22 to 0.40 AU). Kepler-186f receives 32%, placing it within the conservative zone but near the outer edge

The habitable zone can be calculated for any star. If you know the luminosity of the star then it is merely a simple calculation:

ri = √ (Star's Luminosity / 1.1)
ro = √ (Star's Luminosity / 0.53)​

According to the paper where the discovery was announced the luminosity of the Kepler-186 M1V star is 0.0412. Which puts the habitable zone of the star at between 0.19353 AU and 0.27881 AU. Yet the paper places the semi-major axis of the planet at 0.3926 AU. Well outside the habitable zone of the star.

The above calculation method is mentioned and linked to in the second link you provided(near the bottom) as an "alternative approach". Judging from the numbers mfb dug up, it is clear that it was the method used.

The above calculation method is mentioned and linked to in the second link you provided(near the bottom) as an "alternative approach". Judging from the numbers mfb dug up, it is clear that it was the method used.

Unfortunately I could not get their calculator to work properly. Every time I entered the values for the star's surface temperature and the star's luminosity, it kept getting reset to Sol's values. However, I am in the process of reading the paper "Habitable Zones Around Main-Sequence Stars: New Estimates." Thanks.